The present invention relates to an image forming apparatus, in which developer images are formed on image carrying bodies, and a printed image is outputted by transferring the developer images to a transfer medium conveyed by means of a conveyor belt.
A quadruple-tandem color copying machine described in U.S. Pat. No. 5,481,338, for example, is known as an image forming apparatus for forming full-color images. The copying machine of this type comprises an endless conveyor belt for conveying recording sheets and four photoconductive drums arranged side by side along the belt.
Toner images of their own colors (yellow, magenta, cyan, and black) are formed on the photoconductive drum, individually, and successively transferred in layers to a recording sheet that is held on the conveyor belt. The transferred toner images are melted and fixed on the recording sheet, whereupon a color image is outputted.
However, the temperature in the image forming apparatus is likely to increase due to the heat generated at the time of fixing, and the structural components arranged inside the apparatus may thermally expand. This being so, it is very difficult to superpose the images of the four individual colors, yellow, magenta, cyan, and black, accurately on one another as they are transferred to the recording sheet, and therefore, to output high-quality images without color drifts or shifts.